<!DOCTYPE html>
<html>
	<head>
		<meta charset="utf-8">
		<title>:empty</title>
		<style>
			div:empty,
			textarea:empty {
				outline: 2px skyblue solid;
			}

			div {
				height: 10px;
				background-color: red;
				width: 40px;
			}

			body>* {
				margin: 10px 0;
			}
		</style>
	</head>
	<body>
		<div>我不空，但楼下是空的</div>
		<div></div>
		<div>
			<!-- 我有注释 -->
		</div>
		<textarea></textarea>
		<textarea placeholder="仅限IE,有placeholder居然也是不空的,输入字也不空" rows="3"></textarea>
	</body>
</html>
